An integrated circuit may contain an extended drain metal oxide semiconductor (MOS) transistor. The extended drain has a drift region adjacent to the channel region of the extended drain MOS transistor, in combination with a field oxide element in the drain region. The extended drain MOS transistor may be a laterally diffused metal oxide semiconductor (LDMOS) transistor, a diffused metal oxide semiconductor (DMOS) transistor or a drain extended metal oxide semiconductor (DEMOS) transistor. Generally, an average doping in the drift region is less than half an average doping density in the source region of the extended drain MOS transistor. The field oxide element may be formed for example by shallow trench isolation (STI) or by local oxidation of silicon (LOCOS). It may be desirable to perform a thermal drive for the drain implant prior to forming the field oxide element, for example to reduce stress buildup around the field oxide element. It may also be desirable to photolithographically align the drain implant pattern and the field oxide pattern directly, for example to minimize gate-drain capacitance in the extended drain MOS transistor. Aligning the field oxide pattern directly to the drain implant may be problematic, due to a lack of topological features in the drain implant. Aligning the drain implant directly to the field oxide requires performing the drain thermal drive after forming the field oxide.